What is a good approach for debugging errors in Views

Couchbase Server
1

I have a view that will stop outputting results, and the only way I’ve been able to troubleshoot it is through trial and error. Is there a better approach to get logs and debug information for a view? I assume its running into JavaScript errors, and I keep trying to guard against them. Is there something equivalent to console.log from a View’s map function? If so, where can I see that output?

Below is the View in question, which gets published through the Sync Gateway, so it gets wrapped by another function.

    function(doc,meta) {
	                    var sync = doc._sync;
	                    if (sync === undefined || meta.id.substring(0,6) == "_sync:")
	                      return;
	                    if ((sync.flags & 1) || sync.deleted)
	                      return;
	                    var channels = [];
	                    var channelMap = sync.channels;
						if (channelMap) {
							for (var name in channelMap) {
								removed = channelMap[name];
								if (!removed)
									channels.push(name);
							}
						}
	                    delete doc._sync;
	                    meta.rev = sync.rev;
	                    meta.channels = channels;

	                    var _emit = emit;
	                    (function(){
		                    var emit = function(key,value) {
		                    	_emit(key,[channels, value]);
		                    };
							(function (doc, meta) {//
  try{
    if (!doc.channels || doc._deleted) return;
      
    doc.channels.forEach(function (channel) {
        emit(channel, doc.DocumentType);
    });
  }
  catch(exception){ 
    //ideally we would log this, but Couchbase doesn't seem to provide a way to d that
  }
}) (doc, meta);
						}());
					}
2

It’s interesting that you are using the doc._sync property in the map function.

Perhaps @jens can shed some light as to wether it’s ok to call doc._sync in the map/reduce functions.

For debugging views, the view engine outputs logs to /opt/couchbase/var/lib/couchbase/logs/views.log and mapreduce_errors.log.

Have you checked those files when debugging your views?

Note: In Sherlock (CB 4.x), you can use console.log in a map function and the output will be written to mapreduce_errors.log.

James

3

@jamiltz: If you define the view through Couchbase Server, then you have to check the _sync property to make sure the doc you’re mapping is a real document and not metadata like an attachment or user account.

@elevine: Call log("...") to log a message from a map function.

4

Thank you @jens. Where would I find the output when using that log
function?

5

Look at the response above mine…

6

@jens I tried calling log from within my map function, but I see the following in the mapreduce_errors.log:

[mapreduce_errors:error,2015-07-21T12:54:49.777,ns_1@127.0.0.1:<0.23888.1631>:couch_set_view_updater:-do_maps/3-fun-0-:743]Bucket `sync_gateway`, main group `_design/dev_skylight`, error mapping document `_sync:local:c2e61b143b8797e48a5f5fe23d0ce29537e29d39` for view `getAllDocuments`: ReferenceError: log is not defined

We are using Couchbase 3.0.1 Community Edition. Is the log function not available for this version?

7

It’s unfortunately not available for 3.0.1. 4.0 Beta is the first that has this function*. That said, since you’re running into this at development time, you can probably use 4.0 to develop, then test/deploy on 3.x.

By the way, I answered you on Gitter as well. There I suggested:
the strategy I used before that @elevine was to put something at the very end of the btree and scan for that, so it was sort of like logging
I think I had [“ZZZDEBUG”] or probably something smarter as my key

* I filed the RFE :smile:

8

Thank you @ingenthr! I’ve been trying out the other method you suggested too.

9

Thanks @elevine @ingenthr. How do i put something at the end of the btree ?

10

That’s no longer needed @lmessinger, there is now a log() function. Check the docs.

11

@elevine I am stuck down with the same issue. Have you resolved the thing how we can show error logs when there is no view?